Patent Literature 1 discloses a valve device forming a ventilation passage of a fuel tank, which is provided with a float that rises when fuel flows into a case to close a valve opening communicating with the passage to the outside of the tank.
In the valve device provided with such a type of float, when the fuel flows out of the case containing the float in the closed state, the float is able to fall down and transitions to an open state. However, in a case where a pressure difference between in and out of the fuel tank is large, the upper portion of the float may be attached to the valve opening. Therefore, the transition to the open state may not be performed smoothly.
In the technique of Patent Literature 1, the valve opening is closed by a plate-shaped valve body which is provided to obliquely move in the upper portion of the float body. Therefore, in the technique of Patent Literature 1, a close contact between the valve body and the valve opening can be released from the lower side of the obliquely-moving valve body. Even in a case where a pressure difference between in and out of the fuel tank is large, the transition to the open state can be smoothly made.
When the transition to such an open state is made, it is desirable that the air in the tank smoothly flows out of the tank. However, in the technique of Patent Literature 1, the valve body is formed in a simple plate shape in which the width is larger than that of the valve opening, and the gas outflow from the tank immediately after the valve is opened is restrictively performed through a gap between the valve body and the valve opening.